The bacteria of the genus Gallionella belong to the so-called "iron bacteria," which some say literally ‘eat nails.’ Iron bacteria obtain energy for growth by oxidizing a form of iron called ferrous iron (Fe+2) to ferric iron (Fe+3). They have been found everywhere from groundwater to wetlands and deep-sea hydrothermal vents.
Gallionella was first described in the late 1800s. These bacteria as a group have been known to clog drains, water pipes, and wells with deposits of iron oxide compounds. Gallionella ferruginea is often found in iron-bearing mineral springs, water works, wells, and drainages, especially underground drainages in regions near the groundwater table. While it had traditionally been found in fresh water and low-temperature habitats, it has also been found in salt water, marine bays, and thermal springs with temperatures up to roughly 50°C.
(Note: Information adapted from the online version of The Prokaryotes, 1994-2004. Springer-Verlag, New York, LLC. Hans H. Hanert, The Genus Gallionella.